This invention relates to a fuel injection system for supplying fuel to an internal combustion engine of the compression ignition type and having for each cylinder of the engine, a fuel injection nozzle, a reciprocable plunger cam actuated pump which can supply fuel under pressure to the nozzle during inward movement of the plunger in a bore in a pump body, an electromagnetically operable valve means which when closed prevents the spillage of fuel from the bore and a control unit for the valve.